This application claims the priority of German patent document 101 44 076.6, filed 7 Sep. 2001 (PCT International Application No. PCT/EP02/07362, filed 3 Jul. 2002), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for early detection and prediction of damage to assemblies in machine plants, especially mobile machine plants.
Numerous methods and devices are known in for determining the time at which a motor vehicle should be serviced.
For example, German patent document DE 3110774 A1 discloses a method for determining servicing intervals, in which the time for servicing is determined continuously as a function of wear states of the operating variables for which service is to be performed. In this respect, either a single reference variable (for example the lubricating capacity of the engine oil or the state of the brake lining) is used, or further wear states of other operating variables (for example the clutch, carburetor setting, spark plugs, ignition time etc.) are sensed and taken into account in the calculation of the time for a service. The extrapolated time for a service is signaled to the driver by means of a display.
German patent document DE 43 06 270 C1, on the other hand, discloses a method for determining and extending a replacement interval for an assembly by means of at least one operating value which is sensed directly or indirectly and represents the quality state of the operating material. A computing and control unit evaluates at least one operating value, and continuously calculates the replacement interval (and its ratio with respect to a predefined assembly servicing interval), taking into account further sensor data which represent operational values such as the number of starts, number of revolutions of the crankshaft, engine temperature, engine oil pressure, etc.
European patent document EP 0 489 261 A2 discloses a device for calculating a motor vehicle servicing interval based on various sensed and determined operational values such as the number of starts, the revolutions of the crankshaft, the driving times and stationary times, engine temperature, engine oil pressure, charge air pressure, oil consumption, fuel consumption and the like. The calculation result is output audibly and/or visually as a servicing display or instruction. An engine oil refilling process is sensed in terms of quantity and the servicing interval is subsequently extended once by a defined period or a defined odometer reading.
Finally, European patent document EP 0 601 365 B1 discloses a method and apparatus for determining the time for servicing a motor vehicle brake system. Here, the rotational speed and the velocity of the vehicle are determined for each wheel, and the wheel slip is calculated therefrom and stored. If a difference between the wheel slip for various wheels becomes greater than a predefined value, a brake problem signal is generated, and the servicing request is displayed in response to said signal.
In these conventional methods, sensed data obtained on at most one electronic monitoring side are evaluated and assigned to a functional failure, and the time for service is then determined correspondingly.
However, in these conventional methods, no predictive diagnostics are possible. Rather, a time for service is determined from sensor data by reference to faults that are already present; that is, faults which already exist. As a result, only one fault diagnostic operation takes place.
However, methods are also known in which a service interval is determined in a predictive and flexible way.
International patent document WO 99/24699, for example, discloses a method and apparatus for monitoring and/or determining engine oil quality. For this purpose, changes in the viscosity of the oil are determined and evaluated as a function of the temperature and engine friction torque. A control unit for processing and converting recorded data and at least one storage unit are provided for this purpose, and characteristic curves which are necessary for determining the viscosity are stored in one or more storage units. The replacement time for the engine oil is determined as a function of this viscosity data in such a way that the engine is not damaged by inadequate lubrication and cooling.
Furthermore, European patent document EP 1101971 A1 discloses a method for performing diagnostics based on the state of components which are subject to continuous wear, for example brake linings. Here, the wear state is sensed using sensors, and an alarm is issued if the value drops below a predetermined value.
European patent document EP 0764244 B1 discloses a brake-lining-wear measuring system in which wear is sensed by means of a displacement sensor. In this system it is sensed when a new unused brake lining is used, and a new reference value for wear measurements is then correspondingly generated. Subsequently, in response to the new reference value, a wear limit, which represents an acceptable minimum brake lining thickness determined by subtracting the known thickness of the new linings from the new reference value, is generated and stored. In this way, in determining the wear limit, the system takes into account the disk thickness or drum thickness, which decreases throughout the service life of the brake. The expected remaining distance is predicted based on the past wear profile and the remaining lining thickness, and output via a servicing diagnostic system.
However, these methods also permit only one prediction regarding the aging of the lubricant, and the wear of susceptible parts such as brake linings and clutch lining. Moreover, the state of the purely mechanical components of an assembly cannot be determined sufficiently by means of these conventional methods.
In contrast, methods for the early detection of damage are known, for example, in the field of power plant technology or for monitoring machinery in large plants. Out of the necessity to avoid unscheduled down times in large power plants due to the sudden failure of components, methods have been developed which permit the early detection of damage to assembly components, without the component's already exhibiting the conspicuous functional fault. Based on the results which are determined by these methods, it is then possible to decide whether a specific component must be replaced in the next planned machinery downtime for carrying out servicing, or can still continue in use.
German patent document DE 195 45 008 C2 discloses a method for monitoring periodically operating machines, for the early detection of changes. For this purpose, measuring signals which are specific to the machines are sensed by a monitoring sensor, and processed in an evaluation unit with a reference (i.e., measuring signals which are representative of a new machine). In particular, a frequency spectrum derived from the time signals supplied by the sensor is calculated by means of a Fourier transformation for the machine cycle, using frequency signals of at least two, (preferably at least ten), frequency spetra. Mean values of the individual frequency assignment, which form the basis for the monitoring method, are also calculated in the same manner. A sensed change may be indicative of to an irregularity in a fabrication process which results in a change in behavior in the machine, and/or damage to a machine. This change in the machine is displayed.
European patent document EP 0413845 B1 discloses a method for the early detection of damage to machine components, in particular on roller bearings. In this method, forced vibrations of a machine owing to damage to a roller bearing are sensed using a vibration pickup. A digitized signal is generated from this measured signal (for example, the measured acceleration), and decomposed into periodically determined signal components, periodically recurring components with stochastic amplitude, and generally stochastic components. Then, the signal components are analyzed as a function of frequency in order to determine characteristic variables relating to the stressing of the machine component. For this purpose, the frequency spectrum is preferably determined as a spectral power density. Damage-determining intensities for the specific frequency ranges are determined by means of frequency analyses, with the magnitude, scope and form of the frequency distribution being determined. Linking the frequency range and frequency distribution results in a stress factor for the roller bearing. The stress characteristic variables which are determined are compared with characteristic variables for tolerable stress of the machine component to determine the type of damage and/or to determine a degree of damage.
However, hitherto no device or method has been known for early detection and prediction of failures for nonfixed (i.e., mobile) assemblies. In particular, the conventional devices and methods which are explained above are not designed for use in assemblies which are subject to dynamic stress profiles and are operated in a mobile fashion.